Contact finger



H. R. CORNFIELD CONTACT FINGER Nov. 17, 1931.

Filed 001:. 1, 1925 Fig,

INVENTOR Howard E Camfie/d.

TORNEY WITNESSES:

Patented Nov. 17, 1931 PATENT OFFICE HOWARD R. GORNFIELD, OF PITTSBURGH,

PENNSYLVANIA, ASSIGNOR T0 WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA.

oonrnc'r FINGER Application filed October 1, 1925. Serial No. 59,837.

My invention relates to circuit interrupters and particularly to contact fingers therefor.

One object of my invention is to provide a contact finger that shall be capable of moving relatively to its supporting structure.

Another object of my inventionis to provide a contact finger that shall be self-aligning with respect to its cooperating contact member and, at the same time, shall insure a working contact pressure. 7 r

In circuit interrupters, electrical contact is customarily made between a stationary contact member, that frequently comprises a pair of flexible contact fingers, and a movable contact member that is in the form of a blade or wedge. It is essential that the two contact elements shall engage throughout their entire engaging surfaces with a firm working pressure in order to prevent destructive heating and pitting caused by electrical arcs due to imperfect contact. In circuit interrupters, it is difficult to construct and maintain the movable and stationary contact members in proper mechanical and angular relation. It frequently happens that the movable contact member and the stationary contact member are out of alignment by an appreciable number of degrees. In such cases, when the moving contact member is brought into engagement with the stationary contact members, an imperfect contact is made.

I propose to eliminate the foregolng difliculties by mountingthe contact members of the contact fingers loosely on their .gulding membersand, at the same time, subject the contact members to suflicient pressure to maintain their working contact pressures.

In the accompanying drawings, Fig. 1 is a view, in elevation, of a pair of contact fingers embodying my invention in the positions they normally occupy when a circuit inter- V rupter is in its open-circuiting position. 7

Fig. 2 is a view, partially in elevation and partially in section, of the contact fingers when the movable contact members is in engagement therewith.

Fig. 3 is a sectional view of a contact finger, taken longitudinally thereof.

My invention comprises, in general, a pair of contact members 1 that are Carried by a V pair of guiding straps 2 by means of studs 4 and 5, one of which is in engagement with biasing springs 6 for transmitting pressure to the contact members. The stud 4 includes a shank portion 22 of relatively small diameter and a shank portion 14 of relatively large diameter, a shoulder 11 being formed intermediate of said shank portions. The stud 5 likewise includes a small shank portion 23, a large shank'portion 15, and a shoulder 12.

Each of the contact members 1 comprises a contact face 7 of copper, or of other conducting material, to which is secured a suitable conducting lead 8 by means of a plate 9. The lead 8 and the plate 9 are secured on the small shank portions 22 and 23 between the shoulders 11 and 12 and the contact face 7.

The shank portions 14 and 15 extend through openings 16 in the guide member 2 of such diameter as to permit the shank portions 14 and 15 to move relatively thereto;

that is, the openings 16 are of greater diameter than the shank portions 14 and 15. The shank portions 14 and 15 are of greater length than the thickness of the guide member 2. By reason of the loose fit between the shank portions 14 and 15 and the edges of the openings 16, the contacting faces 7 have movement relative to the guide members 2 about their longitudinal and center axes. That is,

the loose connection of the contact face 7 with the guide member 2 permits the contact face to move angularly.

The studs 4 and 5 terminate in rounded heads 18 and 19, respectively. The biasing springs 6 engage the rounded heads 18 of the studs 4 and normally tend to force them infwardly. The contact fingers are normally supported at the end of an insulating bushing or the like (not shown), to which they are secured by suitable bolts 20.

Referring to Fig. 2, the movable contact member 21 is shown in engagement with the contact faces 7 The contact member 21 is shown as being misshapen or out of alignment by the differences between its dotted-line outline and its full-line outline.

By reason of the flexible connection between the guide member 2 and the studs 4 and .5, thecontact faces 7 have turned about their sure of the springs is exerted directly upon the contact faces 7 without the loss of any pressure in flexing the guide member 2, such as would be necessary were a stlif engagement had between it and the studs i and 5. By

reason of the rounded heads 18 on the studs 1, the pressure of the biasing springs 6 is always normal to the engaging surface of the studs 4 which prevents loss of pressure by reason of poor engagement between the springs 6 and the studs 4.

I have found that, where a stiff engage ment is had between the guide member 2 and the'studs 4, and 5, the maximum deflection of the contact faces 7 obtainable about either of its axes was in the neighborhood of 3 or l degrees. However, with the use of my con tact finger, it is possible to secure working engagement between fixed and movable contact members that are as much as 13 degrees out of alignment.

It will thus be seen that I have provided a contacting finger that is flexible and, at the same time, exerts a firm and regular engaging pressure upon its cooperating contact member throughout their entire contacting areas.

It is to be understood that such changes may be made in the structure and arrangement of the several parts as shall fall within the scope of theappended claims.

I claim as my invention:

1. In an electric switch, the combination of cooperating relatively movable first and second contact members, a flexible conductor solidly connected to the first contact member, a guide member having an opening therein for supporting the first contact member, a stud connected at one end to the first contact member, having a head at the other end, and an intermediate shank portion extending through the opening in the guide member, said shank portion being of smaller diameter than said opening and of greater length than the thickness of the guide member adjacent the opening to permit limited angular move ment of the first contact member so that it may adjust itself to the second contact member and engage the same throughout the contacting surfaces, and a spring engaging the head of the stud and biasing the first contact member away from the guide member and against the second contact member.

2. In an electric switch, the combination of a contact structure and a cooperating relatively movable contact, said contact structure comprising a base portion and'two contact fingers carried thereby in opposed relation for engagement with the opposite sides of the cooperating contact, each contact finger comprising a contact member, a flexible conductor rigidly connected to the contact member, a guide member fixed at one end to the base portion and having an opening therein for supporting the contact member, a stud fixed to the contact member and having a shank portion extending through the opening in the guide member, said shank portion being of smaller diameter than the opening in the guide member and of substantially greater length than the thickness of the guide member adjacent the opening to provide for lim ited angular movement of the contact member and translatory movement thereof longitudinall of the stud, and a leaf spring fixed to the ase portion for biasing the contact member against the cooperating contact, the freedom of angular movement permitting the contact member to align itself under influence of the spring with the surface of the cooperating contact and provide engagement of the contact surfaces throughout their contact area.

3. In an electric switch, the combination of a contact structure and a cooperating relatively movable contact, said contact structure comprising a base portion and two contact fingers carried thereby in opposed relation for engagement with the opposite sides of the cooperating contact, each contact finger comprising a contact member, a flexible conductor rigidly connected to the contact member, a guide member fixed at one end to the base portion and having an opening therein for supporting the contact member, a stud fixed to the contact member and having a shank portion extending through the opening in the guide member, said shank portion being of smaller diameter than the opening in the guide member and of substantially greater length than the thickness of the guide member adjacent the opening to provide for limited angular movement of the contact member and translatory movement thereof longitudinally of the stud, and a leaf spring fixed to the base portion and engaging the end of the stud on the side of the guide member opposite from the contact member for biasing the latter away from the guide member and against the cooperating contact, the freedom of angular movement permitting the contact member to alignitself under influence of the spring with the surface of the cooperating contact and provide engagement of the contact surfaces throughout their contact area.

4. In an electric switch, the combination extending through the opening in the guide member, a shoulder between the shank portions, and a head at the end of the large shank portion; said stud being solidly connected at the end adjacent the smaller shank portion to the first contact member; a flexible conductor secured between the first contact member and said shoulder; a biasing member engaging said head and biasing the contact member away from the guide member and against the second contact member, said larger shank portion being of smaller diameter than the opening in the guide member and being of greater length than the thickness of the guide member adjacent said open ing to permit limited angular movement of the first contact member under pressure of the biasing means to align itself with the second contact member and provide engagement of said contact members throughout thelr contacting surfaces.

In testimony whereof, I have hereunto subscribed my name this 24th day of September,

HOWARD R. CORNFIELD. 

